Method for assigning frequencies to base stations of a mobile telephone network

ABSTRACT

The invention relates to a method for allocating frequencies to base stations in a mobile telephone network, especially a method for automatically resetting frequencies already allocated in the case of non-saturated base stations and re-allocating frequencies to said base stations. Firstly, frequencies are allocated to base stations using any known prior art method. In the case where no non-saturated base station is present, a complete frequency plan is obtained. However, if some base stations are not saturated, the inventive method is carried out: the current frequency allocation is reset and a new frequency allocation is carried out automatically. A parameter, the resetting extent parameter, is used to determine to which extent the resetting method is implemented.

[0001] The invention relates to a method for allocating frequencies tobase stations in a mobile telephone network, and in particular to amethod for automatically resetting already allocated frequencies in theevent of non-saturated base stations and reallocating frequencies to thebase stations.

[0002] In conjunction with the expansion of an existing mobile telephonenetwork, for example by adding new base stations, it may happen thatseveral of the newly added base stations are non-saturated after afrequency has been allocated, which is typically performed with the helpof EDP-supported methods. In other words, a lesser number of frequenciesthan required are (can be) allocated to the base stations.

[0003] There are essentially two reasons why these base stations arenon-saturated after a method for allocating frequencies has beenapplied. On one hand, it may involve base stations which cannot reachsaturation due to a combination of the network structure and theplanning parameters; on the other hand, it may involve base stationswhich cannot receive the allocation of the desired number of frequenciesthat are free from interference due to earlier allocations offrequencies to “old” base stations. In the second case, there remains inprinciple the possibility to achieve a saturation of the base stationsby retuning “old” frequency allocations, which would then allow anallocation of frequencies to the newly added stations. This secondpossibility has hitherto been performed manually by the mobile networkplanners. Manual processing not only requires that stations preventingan allocation are identified, but also requires determination of anoptimal new allocation of frequencies.

[0004] It is an object of the present invention to provide a methodwhich automatically allocates the respective number of requiredfrequencies to non-saturated base stations, as far as this is possible.

[0005] This object is solved by the features recited in claim 1.

[0006] Advantageous features and modifications of the method are recitedin the dependent claims.

[0007] The method is preferably implemented in the form of software.

[0008] Advantageously, the described method automatically recognizesthose base stations whose frequencies prevent new allocations, and

[0009] cancels these existing allocations,

[0010] automatically replaces the canceled frequency allocations withnew frequencies, and

[0011] allocates frequencies to the originally non-saturated basestations.

[0012] This significantly simplifies the tasks of the mobile networkplanners, since the method is executed entirely automatically, thuseliminating the need for a manual frequency allocation.

[0013] An embodiment of the invention will be described in more detailhereinafter with reference to the drawings. This results in additionalfeatures, advantages and applications of the method.

[0014] It is shown in:

[0015]FIG. 1 a functional process flow of the frequency allocation withautomatic resetting and reallocation;

[0016]FIG. 2 an illustration of different resetting depths (ring depths)with reference to a cellular mobile telephone network.

[0017] Frequency allocation is directed to allocation of frequencies tobase stations (BS). The allocation must satisfy certain boundaryconditions which essentially reduce interference in a mobile telephonenetwork.

[0018] A BS typically requires more than one frequency.

[0019] The frequencies required at a base stations are initiallyassigned a priority. The frequencies are allocated to the base stationsin the order of their priority. Frequencies with the highest priorityare allocated to important control channels (e.g., BCCH: BroadcastControl Channel). Thereafter, the frequencies with a second priority forthe traffic channels (TCH: Traffic Channel) and frequencies with a thirdpriority for other channels (e.g., HTCH) are allocated.

[0020] Example: a base station requires four frequencies. Aprioritization can look as follows: the base station requires onefrequency of the Priority 1, one frequency of the Priority 2 and twofrequencies of the Priority 3.

[0021] In this case, first a frequency of the Priority 1 is allocated tothe base station. If an allocation is successful, i.e., the frequencycould be allocated to the BS, then a frequency of the Priority 2 isallocated to the BS. Thereafter, if the allocation of the frequency withthe Priority 2 was successful, two frequencies of the Priority 3 areallocated to the BS.

[0022] Hereinafter, the frequencies with the different prioritizationswill be referred to as P1 (Priority 1), P2, P3, etc. In general,frequencies of the Priority 1 have to be allocated before frequencieswith the Priority 2 are allocated, etc.

[0023] The functional process flow is illustrated in FIG. 1: initially,a known conventional method is used to allocate the frequencies. Ifthere are no non-saturated base stations, a complete frequency plan isobtained. Conversely, if non-saturated base stations exist, then themethod according to the invention is executed, i.e., the existingfrequency allocation is reset and frequencies are subsequentlyautomatically reallocated. The extent of the resetting process iscontrolled, inter alia, by a parameter, the resetting depth parameter.

[0024] The basic principle of the method for resetting frequenciesincludes essentially four steps:

[0025] Step 1: it is first checked if combiner separations prevent asaturation of the station. If this is a case, then the correspondingfrequencies are reset and reallocated, thereby increasing the degree ofsaturation of the station. The term combiner separation refers to theseparation between frequencies used at a base station. Exceedinglystrong interferences between the frequencies can be prevented by settinga certain fixed combiner separation.

[0026] Example: the frequency 16 is allocated to a station as a P1frequency, but the station requires another P2 frequency. In thisexample, the set of available frequencies is assumed to be {14, 15, 16,17, 18}, and the combiner separation is assumed to be equal to 3. Allfrequencies are assumed to be essentially acceptable as both P1 and P2frequencies. However, the frequencies 14, 15, 17 and 18 cannot beallocated as P2 frequencies due to the combiner separation.Consequently, no P2 frequency can be allocated to the station. However,retuning the P1 frequency from 16 to 14 makes it possible to allocatethe frequency 17 as a P2 frequency. Accordingly, the frequencies 14 and17 can now be allocated to the station as P1 and P2 frequencies,respectively.

[0027] Step 2: if the first step is not successful, i.e., if no P2frequency can be allocated to the base station in this step, then it ischecked in a second step if—depending on the allocation mode—a Pn+1,Pn+2, Pn+3, etc., frequency meets the quality requirements for a Pnfrequency, i.e., a frequency with a higher priority. If this is thecase, then the corresponding frequency is retuned, for example, a P2frequency is elevated to a P1 frequency. If feasible, the retunedfrequency is newly allocated. In general, a Pn frequency may be retunedas a Pn−1, Pn−2, . . . , P1 frequency.

[0028] Example: assuming there is a station to which the frequency 16was allocated as a P2 frequency. The station still requires a P1frequency. Be the set of the allowed frequencies {14, 15, 16, 17, 18},with the combiner separation being equal to 3. It will be assumed thatthe frequencies 14, 15, 17 and 18 are not to be permissible for the basestation under consideration due to allocations to other stations. If thefrequency 16 also has P1 quality, then it is retuned to the P1frequency. However, the BS then no longer has a P2 frequency. If therewas another frequency that was permissible at the station as a P2frequency, then the method would also allocate this frequency. The BSwould then also have a P2 frequency.

[0029] Step 3: if the previous step is not successful, then frequenciesare reset at stations that have a direct interference relationship withthe actual station and hence prevent an allocation to the actualstation. FIG. 2 shows schematically a detail of a cellular mobiletelephone network, which includes a plurality of wireless cells 1, 2, 3,which are each supplied with radio signals by at least one base station(not shown in detail). The base stations have a mutual interferencerelationship, wherein base stations 2 located immediately adjacent to abase station 1 have typically a direct interference relationship withthe corresponding base station, whereas more distal base stations 3 havetypically only an indirect interference relationship with the basestation 1. If a required frequency cannot be allocated to acorresponding station 1 solely due to pair-wise interferencerelationships, then the frequencies of the stations 2 that prevent thisallocation are reset. This is performed by an algorithm if replacementfrequencies could already been allocated to those stations that had beenreset. This is referred to as resetting with the resetting depth 1 (ringdepth 1).

[0030] Example: it will be assumed that a station A requires a P1frequency. Be the frequencies set {14, 15, 16, 17, 18}, and combinerseparation equal to 3. The frequencies 14 and 18 are assumed not to beallocatable based on a coordination obligation at that station. The termcoordination obligation refers to limitations in the frequency selectionand use at borders between countries. The frequency 16 was allocated toan interfering station B as a P1 frequency. Accordingly, the frequencies15, 16 and 17 cannot be allocated to the station A. In this case, theresetting method resets the P1 frequency of the interfering station,allocates for example the frequency 16 to the station A and subsequentlyallocates the frequency 14 to the station B. However, if no replacementfrequency can be allocated to the interfering station, then the stationA remains non-saturated and the frequency at the station B that wasreset is again allocated. This example is graphically illustrated inTable 1. The various columns indicate the existing frequency spectrum.The rows show the frequency situation at the stations A and B before andafter automatic resetting and reallocation. Frequencies 14 15 16 17 18Station A: L N N N L Station B: C C X C C Station A: N N X C L StationB: X N N N *

[0031] Step 4: if the previous step was also not successful and if theresetting depth parameter is greater than 1, then the frequencies arereset at those neighboring stations 3 that previously prevented anallocation by an indirect interference relationship with the respectivebase station 1.

[0032] The following statement can be made with reference to theprevious example: if a frequency cannot be allocated to the interferingstation B due to the interfering station B due to the other stations(interfering stations), then the frequencies of the interferes ofstation B are reset. Frequencies are thereafter allocated to all thosestations where frequencies had been reset.

[0033]FIG. 2 shows the base station 3 with resetting depth 2.

[0034] The frequencies are generally allocated for the frequencyrequirements of a selected priority. The resetting process treats BSwith non-saturated frequency requirements with respect to priority inthe same way as with respect to frequency allocation. However,frequencies with priorities other than those of the frequency allocationstep can also be retuned. If several valid solutions for one of theaforedescribed steps are determined, then the solution with the smallestnumber of reset frequencies is selected. If several solutions with thesame number of frequencies to be reset exist, then the quality of thefrequencies to be reset controls. Preferably, Pn frequencies are resetbefore Pn−1 frequencies are reset.

1-8. (Canceled)
 9. A method for automatically resetting and reallocatingfrequencies to non-saturated base stations of a mobile telephonenetwork, comprising the steps of (a) checking if combiner separationsprevent a saturation of the base station and, if this is the case, thenthe corresponding frequencies are reset and reallocated; (b) checking ifa frequency could not be allocated to the base station in the previousstep, if—depending on the allocation mode—a Pn+1 frequency has thequality requirements for a Pn frequency, and, if this is the case, thecorresponding frequency is retuned and the frequencies are reallocated;(c) resetting, in the event that no frequency could be allocated to thebase station in the previous steps, frequencies at least one neighboringbase station, which have a direct interference relationship with theparticular base station and which prevent a frequency allocation to theparticular station, whereby frequencies of the particular base stationand the neighboring base station are reallocated; (d) resetting, in theevent that no frequency could be allocated to the base station in theprevious steps, the frequencies at least one neighboring base station,which prevents an allocation by an indirect interference relationshipwith the particular base station, whereby frequencies are reallocated tothe particular base station and the neighboring base station.
 10. Themethod according to claim 9, wherein in the event that no replacementfrequency could be allocated to the neighboring base station accordingto the step (c) or (d), the particular base station remainsnon-saturated and the reset frequency is reallocated to the neighboringbase station.
 11. The method according to claim 9, wherein, if noreplacement frequency could be allocated to the neighboring base stationdue to other base stations, the corresponding frequencies of the otherbase stations that interfere with the neighboring base stations arereset, whereby subsequently the frequencies are reallocated at all thosestations where frequencies had been reset.
 12. The method according toclaim 9, wherein the frequencies are generally allocated according tothe frequency requirements with a selected priority.
 13. The methodaccording to claim 9, wherein the resetting process treats BS withnon-saturated frequency requirements with respect to priority in thesame way as with respect to frequency allocation.
 14. The methodaccording to claim 9, wherein frequencies with a priority other thanthat of the actual frequency allocation step can also be retuned. 15.The method according to claim 9, wherein, if several valid solutions aredetermined for one of the steps (a) through (d), the solution with thesmallest number of frequencies to be reset is selected.
 16. The methodaccording to claim 9, wherein, if there are several solutions with thesame number of frequencies to be reset, then the quality of thefrequencies to be reset determines the selection of the solution,whereby frequencies with the priority Pn are preferably reset before thepriorities Pn−1.